Magnetodielectric y-phase strontium hexagonal ferrite materials formed by sodium substitution

ABSTRACT

Disclosed herein are embodiments of an enhanced resonant frequency hexagonal ferrite material and methods of manufacturing. The hexagonal ferrite material can be Y-phase strontium hexagonal ferrite material. In some embodiments, sodium can be added into the crystal structure of the hexagonal ferrite material in order to achieve high resonance frequencies while maintaining high permeability.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This Application is a continuation of U.S. application Ser. No.14/887,680, filed Oct. 20, 2015, titled “MAGNETODIELECTRIC Y-PHASESTRONTIUM HEXAGONAL FERRITE MATERIALS FORMED BY SODIUM SUBSTITUTION,”which claims from the benefit of U.S. Provisional Application Nos.62/068,147, filed Oct. 24, 2014, titled “INCREASED RESONANT FREQUENCYALKALI-DOPED Y-PHASE HEXAGONAL FERRITES,” 62/068,139, filed Oct. 24,2014, titled “INCREASED RESONANT FREQUENCY POTASSIUM-DOPED HEXAGONALFERRITE,” 62/068,146, filed Oct. 24, 2014, titled “MAGNETODIELECTRICY-PHASE STRONTIUM HEXAGONAL FERRITE MATERIALS FORMED BY SODIUMSUBSTITUTION,” and 62/068,151, filed Oct. 24, 2014, titled“INCORPORATION OF OXIDES INTO FERRITE MATERIAL FOR IMPROVEDRADIOFREQUENCY PROPERTIES,” the entirety of each of which isincorporated herein by reference.

BACKGROUND Field

Embodiments of the disclosure relate to methods of preparingcompositions and materials useful in electronic applications, and inparticular, useful in radio frequency (RF) electronics.

Description of the Related Art

For magnetodielectric antenna applications, it can be advantageous tohave as high a permeability as possible (for better miniaturizationfactor and impedance match in free space) and as great a resonantfrequency (maximum operating frequency) as possible. However, materialsknown in the art with higher permeability tend to have low magneticresonance frequencies, such as a resonant frequency well above 1 GHz buta permeability of only 2.

Some previous solutions have increased permeability, but are limited toa maximum useable frequency of about 500 MHz. Some modest improvementsof resonant frequencies have been detailed, though they have notsignificantly extended the useable frequency range for hexagonal ferritematerials.

Further, it can be advantageous to miniaturize antenna systems able tooperate at frequencies of 500 MHz or above. One method of achieving thisminiaturization is to use magnetodielectric antennas where theminiaturization factor is proportional to the square root of the productof the permeability and permittivity at a given frequency. In this case,the magnetic interaction with RF radiation is utilized to miniaturizethe antenna along with the dielectric component. Other considerationsare that the material must be insulating and that it is advantageousthat the permittivity and permeability be as close to one another aspossible to minimize the impedance mismatch and reflection losses). Onebarrier for improved materials is that there are no insulating magneticmaterials with a permeability above 700 MHz with appreciably low losses.Improving either the permeability at a given frequency or increasing themagnetic Q will increase the frequency of use of magnetodielectricantennas into the commercially and militarily important microwaveregion.

SUMMARY

Disclosed herein are embodiments of a magnetodielectric hexagonalferrite comprising a y-phase strontium hexagonal ferrite material havingsodium substituted for strontium and including a trivalent ortetravalent ion to form a magnetodielectric hexagonal ferrite, thecomposition of the magnetodielectric hexagonal ferrite beingSr_(2-x)Na_(x)Co_(2-x)M_(x)Fe₁₂O₂₂ when a trivalent ion is used, where Mis a trivalent ion, and the composition of the magnetodielectrichexagonal ferrite being Sr_(2-2-2x)Na_(2x)Co_(2x)N_(x)Fe₁₂O₂₂ when atetravalent ion is used, where N is a tetravalent ion.

In some embodiments, M can be selected from the group consisting of Al,Ga, Sc, Cr, Mn, In, Yb, Er, Y or other lanthanide. In some embodiments,N can be selected from the group consisting of Si, Ge, Ti, Zr, Sn, Ce,Pr, Hf, or Tb. In some embodiments, x can be from 0 to about 1.5 in thetrivalent substitution and from 0 to about 0.75 in the tetravalentsubstitution.

In some embodiments, the magnetodielectric hexagonal ferrite can havethe composition Sr_(1.75)Na_(0.25)Co_(1.75)M_(0.25)Fe₁₂O₂₂. In someembodiments, the magnetodielectric hexagonal ferrite can have thecomposition Sr_(1.5)Na_(0.5)Co_(1.5)M_(0.5)Fe₁₂O₂₂.

In some embodiments, the loss factor of the magnetodielectric hexagonalferrite can remain below 4 at frequencies up to 1 GhZ. In someembodiments, the magnetodielectric hexagonal ferrite can have apermeability of between around 5 and around 6 up to 1 GhZ.

Also disclosed herein are embodiments of a method for improving magneticproperties of a hexagonal ferrite material comprising substitutingsodium into a y-phase strontium hexagonal ferrite material for strontiumand charge balancing either using a trivalent or tetravalent ion to forma magnetodielectric hexagonal ferrite, the composition of themagnetodielectric hexagonal ferrite beingSr_(2-x)Na_(x)Co_(2-x)M_(x)Fe₁₂O₂₂ when a trivalent ion is used, where Mis a trivalent ion, and the compositions of the magnetodielectrichexagonal ferrite being Sr_(2-2-2x)Na_(2x)Co_(2x)N_(x)Fe₁₂O₂₂ when atetravalent ion is used, where N is a tetravalent ion.

In some embodiments, M can be selected from the group consisting of Al,Ga, Sc, Cr, Mn, In, Yb, Er, Y or other lanthanide. In some embodiments,N can be selected from the group consisting of Si, Ge, Ti, Zr, Sn, Ce,Pr, Hf, or Tb. In some embodiments, x can be from 0 to about 1.5 in thetrivalent substitution and from 0 to about 0.75 in the tetravalentsubstitution.

In some embodiments, the magnetodielectric hexagonal ferrite can havethe composition Sr_(1.75)Na_(0.25)Co_(1.75)M_(0.25)Fe₁₂O₂₂. In someembodiments, the magnetodielectric hexagonal ferrite can have thecomposition Sr_(1.5)Na_(0.5)Co_(1.5)M_(0.5)Fe₁₂O₂₂.

In some embodiments, the loss factor of the magnetodielectric hexagonalferrite can remain below 4 at frequencies up to 1 GhZ. In someembodiments, the magnetodielectric hexagonal ferrite can have apermeability of between around 5 and around 6 up to 1 GhZ.

Also disclosed herein are embodiments of a magnetodielectric antennacomprising a y-phase strontium hexagonal ferrite material having sodiumsubstituted for strontium and including a trivalent or tetravalent ionto form a magnetodielectric hexagonal ferrite, the composition of themagnetodielectric hexagonal ferrite being Sr_(2-x)Na_(x)Co_(2-x)M_(x)Fe₁₂O₂₂ when a trivalent ion is used, where M is a trivalent ion,and the composition of the magnetodielectric hexagonal ferrite beingSr_(2-2-2x)Na_(2x)Co_(2x)N_(x)Fe₁₂O₂₂ when a tetravalent ion is used,where N is a tetravalent ion.

In some embodiments, M can be selected from the group consisting of Al,Ga, Sc, Cr, Mn, In, Yb, Er, Y or other lanthanide. In some embodiments,N can be selected from the group consisting of Si, Ge, Ti, Zr, Sn, Ce,Pr, Hf, or Tb. In some embodiments, x can be from 0 to about 1.5 in thetrivalent substitution and from 0 to about 0.75 in the tetravalentsubstitution.

In some embodiments, the magnetodielectric hexagonal ferrite can havethe composition Sr_(1.75)Na_(0.25)Co_(1.75)M_(0.25)Fe₁₂O₂₂. In someembodiments, the magnetodielectric hexagonal ferrite can have thecomposition Sr_(1.5)Na_(0.5)Co_(1.5)M_(0.5)Fe₁₂O₂₂.

In some embodiments, the loss factor of the magnetodielectric hexagonalferrite can remain below 4 at frequencies up to 1 GhZ. In someembodiments, the magnetodielectric hexagonal ferrite can have apermeability of between around 5 and around 6 up to 1 GhZ.

Disclosed herein are embodiments of a method for increasing the resonantfrequency of a hexagonal ferrite material comprising providing a Y phasehexagonal ferrite material having the composition Sr₂Co₂Fe₁₂O₂₂ anddoping the hexagonal ferrite with Na, K or other univalent alkali metalon an Sr site and charge compensating with scandium or indium on acobalt site.

In some embodiments, the hexagonal ferrite material can be doped withsilicon, aluminum, manganese, or any combination of the three. In someembodiments, the hexagonal ferrite can be doped with silicon, and thesilicon acts as a grain growth inhibitor. In some embodiments, thehexagonal ferrite can be doped with manganese, and the manganeseprevents reduction of the iron in the composition to Fe³⁺.

In some embodiments, scandium can be used for charge compensating. Insome embodiments, indium can be used for charge compensating.

In some embodiments, the hexagonal ferrite can have a loss factor ofless than about 6 at a frequency of 1 GHz.

Also disclosed herein are embodiments of a hexagonal ferrite materialhaving enhanced resonant frequency comprising a Y phase hexagonalferrite material having the composition Sr₂Co₂Fe₁₂O₂₂, the materialbeing doped with Na, K or other univalent alkali metal on an Sr site andincluding scandium or indium on a cobalt site.

In some embodiments, the hexagonal ferrite material can be doped withsilicon, aluminum, manganese, or any combination of the three. In someembodiments, the hexagonal ferrite can be doped with silicon, and thesilicon acts as a grain growth inhibitor. In some embodiments, thehexagonal ferrite can be doped with manganese, and the manganeseprevents reduction of the iron in the composition to Fe³⁺.

In some embodiments, scandium can be used for charge compensating. Insome embodiments, indium can be used for charge compensating.

In some embodiments, the hexagonal ferrite can have a loss factor ofless than about 6 at a frequency of 1 GHz.

Also disclosed herein are embodiments of a radiofrequency devicecomprising a Y phase hexagonal ferrite material having the compositionSr₂Co₂Fe₁₂O₂₂, the material being doped with Na, K or other univalentalkali metal on an Sr site and including scandium or indium on a cobaltsite.

In some embodiments, the hexagonal ferrite material can be doped withsilicon, aluminum, manganese, or any combination of the three. In someembodiments, the hexagonal ferrite can be doped with silicon, and thesilicon acts as a grain growth inhibitor. In some embodiments, thehexagonal ferrite can be doped with manganese, and the manganeseprevents reduction of the iron in the composition to Fe³⁺.

In some embodiments, scandium can be used for charge compensating. Insome embodiments, indium can be used for charge compensating.

In some embodiments, the hexagonal ferrite can have a loss factor ofless than about 6 at a frequency of 1 GHz.

Disclosed herein are embodiments of a method for doping a y-phasehexagonal ferrite material with potassium comprising providing a y-phasestrontium hexagonal ferrite material and substituting at least some ofthe strontium with a trivalent ion composition including potassium or atetravalent ion composition including potassium to form a high resonantfrequency hexagonal ferrite, the composition being Sr_(2-x)K_(x)Co_(2-x)M_(x)Fe₁₂O₂₂ when a trivalent ion is used for the substitution, M beingany trivalent ion, and the composition beingSr_(2-2x)K_(2x)Co_(2-x)N_(x)Fe₁₂O₂₂ when a tetravalent ion is used forthe substitution, N being any tetravalent ion.

In some embodiments, x can be from 0 to 1.5 in the trivalentsubstitution and from 0 to 0.75 in the tetravalent substitution. In someembodiments, the y-phase strontium hexagonal ferrite material caninclude Sr₂Co₂Fe₁₂O₂₂.

In some embodiments, M can be selected from the group consisting of Sc,Mn, In, Cr, Ga, Co, Ni, Fe, Yb, or any of the lanthanide ions. In someembodiments, N can be selected from the group consisting of Si, Ge, Ti,Zr, Sn, Ce, Pr, Hf, or Tb.

In some embodiments, substituting at least some of the strontium withpotassium can include adding potassium carbonate to the y-phasestrontium hexagonal ferrite material.

In some embodiments, the high resonant frequency hexagonal ferrite canhave a loss factor below 1 at 1 GhZ.

In some embodiments, the high resonant frequency hexagonal ferrite canhave a composition of Sr_(1.75)K_(0.25)Co_(1.75)Co_(0.25)Fe₁₂O₂₂ orSr_(1.75)K_(0.25)Co_(1.75)In_(0.25)Fe₁₂O₂₂. In some embodiments, thehigh resonant frequency hexagonal ferrite can have a composition ofSr_(1.5)K_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂ orSr_(1.5)K_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂.

Also disclosed herein are embodiments of an antenna for use inradiofrequency operations comprising a y-phase strontium hexagonalferrite material having at least some of the strontium substituted outfor a trivalent ion composition including potassium or a tetravalent ioncomposition including potassium to form a high resonant frequencyhexagonal ferrite, the composition beingSr_(2-x)K_(x)Co_(2-x)M_(x)Fe₁₂O₂₂ when a trivalent ion is used for thesubstitution, M being any trivalent ion, and the composition beingSr_(2-2x)K_(2x)Co_(2-x)N_(x)Fe₁₂O₂₂ when a tetravalent ion is used forthe substitution, N being any tetravalent ion.

In some embodiments, x can be from 0 to 1.5 in the trivalentsubstitution and from 0 to 0.75 in the tetravalent substitution. In someembodiments, the y-phase strontium hexagonal ferrite material caninclude Sr₂Co₂Fe₁₂O₂₂.

In some embodiments, M can be selected from the group consisting of Sc,Mn, In, Cr, Ga, Co, Ni, Fe, Yb, or any of the lanthanide ions. In someembodiments, N can be selected from the group consisting of Si, Ge, Ti,Zr, Sn, Ce, Pr, Hf, or Tb.

In some embodiments, the potassium can include potassium carbonate.

In some embodiments, the high resonant frequency hexagonal ferrite canhave a loss factor below 1 at 1 GhZ.

In some embodiments, the high resonant frequency hexagonal ferrite canhave a composition of Sr_(1.75)K_(0.25)Co_(1.75)Sc_(0.25)Fe₁₂O₂₂ orSr_(1.75)K_(0.25)Co_(1.75)In_(0.25)Fe₁₂O₂₂. In some embodiments, thehigh resonant frequency hexagonal ferrite can have a composition ofSr_(1.5)K_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂ orSr_(1.5)K_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂.

Also disclosed herein are embodiments of a potassium doped y-phasehexagonal ferrite material comprising a y-phase strontium hexagonalferrite material having at least some of the strontium substituted outfor a trivalent ion composition including potassium or a tetravalent ioncomposition including potassium to form a high resonant frequencyhexagonal ferrite, the composition beingSr_(2-x)K_(x)Co_(2-x)M_(x)Fe₁₂O₂₂ when a trivalent ion is used for thesubstitution, M being any trivalent ion, and the composition beingSr_(2-2x)K_(2x)Co_(2-x)N_(x)Fe₁₂O₂₂ when a tetravalent ion is used forthe substitution, N being any tetravalent ion.

In some embodiments, x can be from 0 to 1.5 in the trivalentsubstitution and from 0 to 0.75 in the tetravalent substitution. In someembodiments, the y-phase strontium hexagonal ferrite material caninclude Sr₂Co₂Fe₁₂O₂₂.

In some embodiments, M can be selected from the group consisting of Sc,Mn, In, Cr, Ga, Co, Ni, Fe, Yb, or any of the lanthanide ions. In someembodiments, N can be selected from the group consisting of Si, Ge, Ti,Zr, Sn, Ce, Pr, Hf, or Tb.

In some embodiments, the potassium can include potassium carbonate.

In some embodiments, the high resonant frequency hexagonal ferrite canhave a loss factor below 1 at 1 GhZ.

In some embodiments, the high resonant frequency hexagonal ferrite canhave a composition of Sr_(1.75)K_(0.25)Co_(1.75)Sc_(0.25)Fe₁₂O₂₂ orSr_(1.75)K_(0.25)Co_(1.75)In_(0.25)Fe₁₂O₂₂. In some embodiments, thehigh resonant frequency hexagonal ferrite can have a composition ofSr_(1.5)K_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂ orSr_(1.5)K_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂.

Disclosed herein are embodiments of a method for incorporatingadditional oxides to increase the magnetic properties of a hexagonalferrite comprising providing a y-phase hexagonal ferrite material andincorporating an oxide consistent with the stoichiometry ofSr₃Co₂Fe₂₄O₄₁, SrFe₁₂O₁₉ or CoFe₂O₄ to form an enhanced hexagonalferrite material.

In some embodiments, the enhanced hexagonal ferrite material can be asingle phase. In some embodiments, the enhanced hexagonal ferritematerial can be two distinct phases.

In some embodiments, the Y-phase hexagonal ferrite material can includeSr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₁O₂₂. In some embodiments, the oxidecan include CoFe₂O₄. In some embodiments, the oxide can includeSrFe₁₂O₁₉. In some embodiments, 2 wt. % of the oxide can be incorporatedinto the y-phase hexagonal ferrite material.

In some embodiments, the enhanced hexagonal ferrite material can have aQ value of greater than about 20 at 800 MHz. In some embodiments, theenhanced hexagonal ferrite material can have a Q value of greater thanabout 15 at 1 GHz.

In some embodiments, the enhanced hexagonal ferrite material can have apermeability of between 6 and 8 from 800 MHz to 1 GHz. In someembodiments, the enhanced hexagonal ferrite material can have adielectric constant of about 10-11.

Also disclosed herein are embodiments of an enhanced hexagonal ferritehaving increased magnetic properties comprising a y-phase hexagonalferrite material, the y-phase hexagonal ferrite material having an oxideconsistent with the stoichiometry of Sr₃Co₂Fe₂₄O₄₁, SrFe₁₂O₁₉ or CoFe₂O₄incorporated within.

In some embodiments, the enhanced hexagonal ferrite material can be asingle phase. In some embodiments, the enhanced hexagonal ferritematerial can be two distinct phases.

In some embodiments, the Y-phase hexagonal ferrite material can includeSr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₁O₂₂. In some embodiments, the oxidecan include CoFe₂O₄. In some embodiments, the oxide can includeSrFe₁₂O₁₉. In some embodiments, 2 wt. % of the oxide can be incorporatedinto the y-phase hexagonal ferrite material.

In some embodiments, the enhanced hexagonal ferrite material can have aQ value of greater than about 20 at 800 MHz. In some embodiments, theenhanced hexagonal ferrite material can have a Q value of greater thanabout 15 at 1 GHz.

In some embodiments, the enhanced hexagonal ferrite material can have apermeability of between 6 and 8 from 800 MHz to 1 GHz. In someembodiments, the enhanced hexagonal ferrite material can have adielectric constant of about 10-11.

Also disclosed herein are embodiments of a radiofrequency antenna foruse in high frequency applications comprising a y-phase hexagonalferrite material, the y-phase hexagonal ferrite material having an oxideconsistent with the stoichiometry of Sr₃Co₂Fe₂₄O₄₁, SrFe₁₂O₁₉ or CoFe₂O₄incorporated within to form an enhanced hexagonal ferrite material.

In some embodiments, the enhanced hexagonal ferrite material can be asingle phase. In some embodiments, the enhanced hexagonal ferritematerial can be two distinct phases.

In some embodiments, the Y-phase hexagonal ferrite material can includeSr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₁O₂₂. In some embodiments, the oxidecan include CoFe₂O₄. In some embodiments, the oxide can includeSrFe₁₂O₁₉. In some embodiments, 2 wt. % of the oxide can be incorporatedinto the y-phase hexagonal ferrite material.

In some embodiments, the enhanced hexagonal ferrite material can have aQ value of greater than about 20 at 800 MHz. In some embodiments, theenhanced hexagonal ferrite material can have a Q value of greater thanabout 15 at 1 GHz.

In some embodiments, the enhanced hexagonal ferrite material can have apermeability of between 6 and 8 from 800 MHz to 1 GHz. In someembodiments, the enhanced hexagonal ferrite material can have adielectric constant of about 10-11.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates permeability and loss factor for an embodiment of aY-phase hexagonal ferrite.

FIG. 2 illustrates the crystal structure of an embodiment of a Y-phasehexagonal ferrite.

FIG. 3 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite without potassium carbonate.

FIG. 4 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite with potassium carbonate.

FIG. 5 illustrates permeability v. frequency for an embodiment of aY-phase hexagonal ferrite.

FIG. 6 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite having scandium andincorporating 0.25 wt. % potassium.

FIG. 7 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite having indium andincorporating 0.25 wt. % potassium.

FIG. 8 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite having scandium andincorporating 0.5 wt. % potassium.

FIG. 9 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite having indium andincorporating 0.5 wt. % potassium.

FIG. 10 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite having scandium andincorporating 0.25 wt. % sodium.

FIG. 11 illustrates permeability and loss factor based on frequency foran embodiment of Y-phase hexagonal ferrite having scandium andincorporating 0.5 wt. % sodium.

FIG. 12 shows an embodiment of a process that can be implemented tofabricate a ceramic material incorporating embodiments of Y-phasehexagonal ferrite.

FIG. 13 shows an embodiment of a process that can be implemented to forma shaped object from powder material incorporating embodiments ofY-phase hexagonal ferrite.

FIG. 14 shows examples of various stages of the process of FIG. 13.

FIG. 15 shows an embodiment of a process that can be implemented tosinter formed objects such as those formed in the example of FIGS. 13and 14.

FIG. 16 shows examples of various stages of the process of FIG. 15.

FIG. 17 illustrates permeability and loss factor for an embodiment of aY-phase hexagonal ferrite.

FIG. 18 illustrates permeability and magnetic Q for an embodiment of aY-phase hexagonal ferrite with an incorporated oxide.

FIG. 19 is a flow chart illustrating an embodiment of a method offorming a hexagonal ferrite material.

FIG. 20 is a flow chart illustrating an embodiment of a method offorming a hexagonal ferrite material.

FIG. 21 is a power amplifier modular which can incorporate embodimentsof the disclosed hexagonal ferrite material.

FIG. 22 is a wireless device which can incorporate embodiments of thedisclosed hexagonal ferrite material.

DETAILED DESCRIPTION

Disclosed herein are embodiments of materials that can be advantageousfor use as magnetodielectric materials. These magnetodielectricmaterials can be particularly useful in radiofrequency (RF) devices suchas antennas, transformers, inductors, circulators, and absorbers becauseof certain favorable material properties. For example, magnetodielectricmaterials disclosed herein can be used at high frequency levels whilemaintaining good qualities, thus increasing the upper frequency limitsof antennas and other devices the material is incorporated into.Additionally, some of the properties afforded by disclosedmagnetodielectric materials can be favorable miniaturizing factors,reduced field concentration, and better impedance match, all of whichare advantageous for radiofrequency devices. Further, as shown in FIG.1, the loss tangent of embodiments of the material can be relativelyminimized until higher resonant frequency spectrums, thus making thematerial advantageous for antennas, especially those who use a varietyof different frequency ranges.

Recent advances in magnetodielectric materials are driven in part by thedesire to miniaturize high frequency antennas, thus reducing the overallfootprint of the antenna, while maintaining desirable bandwidth,impedance, and low dielectric loss. Disclosed herein are materials andmethods of making magnetodielectric materials that have improvedresonant frequencies as well as low dielectric loss, thus providing formaterials that are advantageous for use in, at least, radiofrequencyelectronics. Two figures of merit for antenna performance include theminiaturization factor and the bandwidth. First, the miniaturizationfactor is determined by the formula:

d _(eff) =d _(o)(ε_(r)μ_(r))^(−1/2)

where d_(eff)/d_(o) is the miniaturization factor, ε_(r) is thedielectric constant of the antenna material, and μ_(r) is the magneticpermeability of the antenna material. Both ε_(r) and μ_(r) are dependenton frequency in magnetic oxide antennas. Second the effective bandwidth(or efficiency) is determined by the formula:

η=η₀(μ_(r)/ε_(r))^(−1/2)

where η/η_(o) describes the efficiency (or bandwidth) of the material.This efficiency is maximized if μ_(r) is maximized. In additionμ_(r)=ε_(r) there is a perfect impedance match to free space.

Hexagonal Ferrite

One class of materials that can have advantageous magnetic propertiesfor magnetodielectric applications are hexagonal ferrites. Hexagonalferrites, or hexaferrites, have magnetic properties that can be directlylinked to their crystal structure. For example, hexagonal ferrites allhave magnetocrystalline anisotropy, where the response to an inducedmagnetic field has a preferred orientation through the crystalstructure. Additionally, hexagonal ferrite systems, in particular, canbe desirable because of their high magnetic permeability and absorptionat microwave (100 MHz-20 GHz) frequencies, which are useful antennafrequencies.

Hexagonal ferrite crystal systems can include crystal structures thatare generally intergrowths between magnetoplumbite and spinel structurescontaining strontium (Sr) or barium (Ba), a divalent cation such as iron(Fe), cobalt (Co), nickel (Ni) or manganese (Mn) and trivalent Fe. Thehexagonal ferrite may be formed in a variety of different crystalstructures based on the magnetoplumbite cell. These structures includeM-phase (SrFe₁₂O₁₉), W-phase (BaMe₂Fe₁₆O₂₇), Y-phase (Sr₂Me₂Fe₁₂O₂₂) andZ-phase (Ba₃Me₂Fe₂₄O₄₂), as well as combinations of the structures. FIG.2 illustrates the crystal structure of Y-phase hexagonal ferrite.

While typical hexagonal ferrites contain barium, the barium atoms can besubstituted out for an atom of a similar size, such as strontium.Accordingly, the substitution of the barium atoms with strontium atomsshould not negatively impact the properties of the material as thestructure should retain generally the same shape. In fact, as shownbelow, the use of strontium instead of barium can allow for otherprocessing methods that improve the magnetodielectric properties of thehexagonal ferrite.

One example hexagonal ferrite that can be particularly advantageous as amagnetodielectric material for use in, for example, high frequencyantennas or other RF devices, is Y-phase strontium cobalt ferrite(Sr₂CO₂Fe₁₂O₂₂), commonly abbreviated as Co₂Y. Disclosed herein areembodiments of this a class of Y-phase hexagonal ferrites, as well asmethods of manufacturing them, having improved magnetic propertiesuseful for RF applications, such as improved resonant frequencies, lowmagnetic loss, and high Q factor values.

Embodiments of the present disclosure, teach methods and processingtechniques for improving performance characteristics of hexagonalferrite materials used in high frequency applications. Certainembodiments provide improved methods and processing techniques formanufacturing Y-phase hexagonal ferrite systems Sr₂Co₂Fe₁₂O₂₂ (Co₂Y)that have reduced magnetorestriction, improved resonant frequency, andextended magnetic permeability at higher frequencies.

Magnetodielectric Properties

Certain properties of a material can be advantageous for use inmagnetodielectric applications, such as radio frequency antennas. Theseproperties include, but are not limited to, magnetic permeability,permittivity, magnetic anisotropy, magnetic loss, and magnetic Q values.

Permeability is the measure of the ability of a material to support theformation of a magnetic field within itself. In other words, magneticpermeability is the degree of magnetization that a material obtains inresponse to an applied magnetic field. Accordingly, a higher magneticpermeability, or mu′ or μ′, allows for a material to support a highermagnetic field. Accordingly, it can be advantageous to have highmagnetic permeability for use with radio frequency applications.

Relative permeability and relative permittivity are propertiesindicative of the performance of a magnetic material in high frequencyantenna applications. Relative permeability is a measure of the degreeof magnetization of a material that responds linearly to an appliedmagnetic field relative to that of free space (μ_(r)=μ/μ_(o)). Relativepermittivity (ε_(r)) is a relative measure of the electronicpolarizability of a material relative to the polarizability of freespace (ϵ_(r)=ε/ε_(o)). Generally, permeability (μ′) can be separatedinto two components: spin rotational X_(sp) which is in response forhigh frequency, and domain wall motion X_(dw) which is damped out atmicrowave frequencies. Permeability can be generally represented byμ′=1+X_(dw)+X_(sp).

Unlike spinels, Co₂Y systems typically have a non-cubic unit cell,planar magnetization, and an anisotropic spin-rotation component topermeability. Spin rotation anisotropy is also a consideration inpreparing Co₂Y for high frequency applications. Large anisotropy fields(H_(θ)) are similar to applying an external magnetic field whichincreases resonant frequency, whereas small anisotropy fields (H_(φ))improve permeability. Ho is generally strong in hexagonal ferrites, suchas Co₂Y. As such, domain formation out of the basal plane is suppressedand the material becomes self-magnetizing. The relationship between thepermeability and the rotational stiffness can be represented by theformula (μ₀−1)/4π=(⅓)(M_(s)/H_(θ) ^(A)+M_(s)/H_(φ) ^(A)). For isotropicrotational stiffness (as in spinels), the relationship can berepresented as follows: (μ_(o)−1)/4π=(⅔)(M_(s)/H^(A)). For cases whereH_(θ) ^(A) does not equal to H_(φ) ^(A): f_(res) (μ_(o)−1)=4/3 ψM_(s) [½(H_(θ) ^(A)/H_(φ) ^(A))+½ (H_(φ) ^(A)/H_(θ) ^(A))]. It is believed thatthe larger the difference in rotational stiffness, the greater theself-magnetization field, which could push the resonant frequency intothe microwave region. Permeability drops quickly above the resonancefrequency.

Another property of magnetodielectric antenna materials is the magneticloss factor. The magnetic loss tangent describes the ability of themagnetic response in a material to be in phase with the frequency of theapplied magnetic field (in this case from electromagnetic radiation) ata certain frequency. This is represented as tan δ_(m)=μ″/μ′. TheMagnetic Q is the inverse of the magnetic loss tangent. Q=1/tan δ_(m).For example, if a loss factor is high at a certain frequency, thematerial would not be able to operate at that frequency. Accordingly, itcan be advantageous for a magnetodielectric material to have lowmagnetic loss tangent up to higher frequencies, such as those above 500MHz, above 800 MHz, or above 1 GHz, as the material could then be usedin applications at those high frequencies. Magnetic Q factors of above20 are advantageous for some applications. This can be especially usefulfor antennas to select particular high frequency signals withoutinterference from other signals at around the selected range.

Substitution with Potassium (K)

In some embodiments, improvements to hexagonal ferrite material can bemade by substituting potassium (K) into the crystal structure of theY-phase hexagonal ferrite material. This incorporation can be done with,or without, the other methods for improving magnetic propertiesdiscussed through the disclosure.

In order to increase the resonant frequency of a material, such as theY-phase hexagonal ferrite, small amounts of alkali metals can be dopedinto the composition. For example, lithium, sodium, potassium, andrubidium can all be doped into the hexagonal ferrite. In doing so,strontium atoms can be substituted out to make room for the alkalimetals. This addition of alkali metal can prevent the reduction of ironto the Fe²⁺ state. Since the alkali metal with a 1+ oxidation statesubstitutes for Sr with a 2+ oxidation state, it decreases thelikelihood of Fe³⁺ converting to Fe²⁺ because, in this case, the averagemetal oxidation state becomes too low. Therefore, the reduction of ironduring sintering is inhibited. By avoiding the reduction of iron, thethreshold for the resonant frequency can be pushed higher than valuesthat have been previously obtained. Fe²⁺ decreases the resonantfrequency and contributes to both the magnetic and the dielectric losstangents. Accordingly, the increased resonant frequency, along with thedecreased magnetic loss tangent, can then result in a correspondingincrease in the magnetic Q factor, allowing for embodiments of thedisclosed material to have advantageous uses as a magnetodielectricmaterial.

In some embodiments, potassium (K) may be added as an excess material toSr₂Co₂Fe₁₂O₂₂ in, for example, the form of potassium carbonate. However,other potassium sources can be used as well, and the particularpotassium composition is not limiting. Further, in some embodiments thepotassium can be substituted into the strontium site on the crystalstructure. Potassium carbonate can be added into the structure with theoxide blend in modest amounts and can become incorporated into thestructure, for example during a heat treatment of the material.

Strontium and potassium have different charges to their atoms, 2+ forstrontium and 1+ for potassium (or sodium) and thus some chargebalancing can be used to avoid any significant or harmful distortion ofthe crystal structure of the Y-phase hexagonal ferrite. In someembodiments, a trivalent or tetravalent species can be substituted infor cobalt (having a 2+ charge, similar to the strontium), which cancompensate for the charge imbalance that occurs by substituting K⁺ infor Sr²⁺, thus leading to a generally balanced chemical structure. Dueto the ability to provide charge balancing, two series of compounds canbe used, one for trivalent ion substitutions for cobalt and one fortetravalent ion substitutions of cobalt.

For trivalent ion substitution, the below example composition can beused in certain embodiments:

Sr_(2-x)K_(x)Co_(2-x)M_(x)Fe₁₂O₂₂

where M can be any trivalent ion. For example, M can be Sc, Mn, In, Cr,Ga, Co, Ni, Fe, Yb, Er, Y or any of the lanthanide ions, and theparticular element is not limiting. Further, x values can be in therange of about 0 to about 1.5. In some embodiments, 0.2<x<0.7.

For tetravalent ion substitution, the below example composition can beused in certain embodiments:

Sr_(2-2x)K_(2x)Co_(2-x)N_(x)Fe₁₂O₂₂

where N can be any tetravalent ion. For example, N can be Si, Ge, Ti,Zr, Sn, Ce, Pr, Hf, or Tb, and the particular element is not limiting.Again, in some embodiments x values can be in the range of about 0 to0.75. In some embodiments, 0.2<x<0.5

FIGS. 3-4 show impedance spectra using the above disclosed substitutiontechnique of adding potassium carbonate. Typically, the impedancespectra is performed using dielectric spectroscopy, also known asimpedance spectroscopy or electrochemical impedance spectroscopy. Theimpedance spectra can advantageously show the different dielectricproperties of a medium as a function of different frequencies.

In FIGS. 3-4, the impedance spectra shows both permeability (μ′) as wellas loss factor (μ″) across a range of frequencies. It can beadvantageous for magnetodielectric materials used in radio frequencyapplications to have a minimal change in properties across the range offrequencies, and in particular a minimal μ″, and therefore a minimalloss tangent, at those particular frequencies. When the loss tangentbegins to increase or spike, the material may become unsuitable forantenna applications using that particular range of frequencies.

Along with minimizing the loss tangent spike, it can be advantageous toadjust the spike (or quick increase) in loss tangent to as high afrequency as possible. As mentioned, when the loss tangent spikes, thematerial may become less useful at those particular frequencies. Sohaving a loss tangent spike at higher frequencies can generally meanthat the material can be used at higher frequencies (up until the spike)with minimized loss.

In particular, FIG. 3 illustrates the permeability without theincorporation of potassium carbonate. Accordingly, the composition ispure sintered Sr₂Co₂Fe₁₂O₂₂ without the use of potassium carbonate.

As shown in FIG. 3, the μ″ (loss factor) of the material can vary wildlyat low frequencies. Further, as the frequency increases, μ″ steadilyincreases (after reducing much of the variation of the lowerfrequencies) until it begins a generally exponential growth.

On the other hand, FIG. 4 illustrates the permeability and loss factorfor a Sr₂Co₂Fe₁₂O₂₂ wherein potassium carbonate is added in.

As shown in FIG. 4, the loss factor of an embodiment of the Y-phasehexagonal ferrite material can be lower than the one shown in FIG. 3.Further, the loss factor shown in FIG. 4 actually decreases as thefrequency increases up to a certain point, such as between 1 and 10 MHz.In the ranges of around 100 MHz to about 800 MHz, the loss factorremains relatively stable at about 0.7, before increasing. However, evenat the higher frequency of 1 GHz, the material still has a loss factorof only around 1. Looking back at the previous FIG. 3 without potassiumcarbonate, it is clearly shown that the potassium carbonate additiongreatly reduces the loss factor of the Y-phase hexagonal ferritematerial, making it advantageous for high frequency radiofrequencyapplications.

Further, FIG. 5 shows a graph of permeability v. frequency for anembodiment of the disclosed material without the incorporation ofpotassium carbonate. As shown in FIG. 5, the permeability of thematerial remains relatively constant throughout the frequency rangestested. Generally, the permeability of the material remains just under2.5, though there is some minor increase as the tested frequencyincreases. The permeability increases to over 2.5 at approximately 160MHz.

FIG. 6 illustrates the permeability and loss factor for a hexagonalferrite material discussed above with a trivalent substitution where Mis Sc and where x=0.25.

As shown in FIG. 6, the μ″ (loss factor) of an embodiment of the Y-phasehexagonal ferrite material is extremely low, reaching to almost 0. Evenas the frequency increases to over 1 GHz, the material maintains lossfactors of below 0.5. While maintaining the low loss factor, thematerial shown in FIG. 6 also contains a permeability of around 4.

Further, while maintaining the low loss factor, the material shown inFIG. 6 also contains a permeability of over 3, which is greater than thetypical values for Y-phase hexagonal ferrite materials, and thus canprovide the material with advantageous properties.

Accordingly, because of the low loss factor and the high magneticpermeability, embodiments of the Y-phase hexagonal ferrite materialdiscussed above can be advantageous for use as a magnetodielectricmaterial, such as in a radio frequency antennas or other high frequencyapplications.

FIG. 7 illustrates the permeability and loss factor for a hexagonalferrite material discussed above with a trivalent substitution where Mis In and where x=0.25.

As shown in FIG. 7, the loss factor of an embodiment of the Y-phasehexagonal ferrite material is extremely low, reaching almost to 0. Evenas the frequency increases to over 1 GHz, the material maintains a lossfactor of below 0.5. It is not until over 1 GHz that the loss factor ofthe material begins to spike, and as shown the increase can besignificant after 1 GHz.

Further, while maintaining the low loss factor, the material shown inFIG. 7 also contains a permeability of over 3 (staying around 3.5),which is greater than the typical values for Y-phase hexagonal ferritematerials, and thus can provide the material with advantageousproperties.

Accordingly, because of the low loss factor and the high magneticpermeability, embodiments of the Y-phase hexagonal ferrite materialshown with respect to FIG. 7 can be advantageous for use as amagnetodielectric material, such as in a radio frequency antenna orother high frequency applications.

FIG. 8 illustrates the permeability and loss factor for a hexagonalferrite material having trivalent substitution where M is Sc and wherex=0.5.

As shown in FIG. 8, the loss factor of an embodiment of the Y-phasehexagonal ferrite material is extremely low, reaching almost to 0. Evenas the frequency increases to over 1 GHz, the material maintains lossfactors of below 1. It is not until over 1 GHz that the loss factor ofthe material begins to spike, and as shown the increase can besignificant after 1 GHz.

Further, while maintaining the low loss factor, the material shown inFIG. 8 also contains a permeability of about 3 to about 4, which isgreater than the typical for a Y-phase hexagonal ferrite material.

Accordingly, because of the low loss factor and the high magneticpermeability, embodiments of the Y-phase hexagonal ferrite materialshown with respect to FIG. 8 can be advantageous for use as amagnetodielectric material, such as in a radio frequency antenna orother high frequency applications.

FIG. 9 illustrates the permeability and loss factor for a hexagonalferrite material having trivalent substitution where M is In and wherex=0.5.

As shown in FIG. 9, the loss factor of an embodiment of the Y-phasehexagonal ferrite material is again extremely low, though slightly abovethe other figures described above. The loss factor reduces greatly tonear 0 from about 100 MHz to about 800 MHz, when the loss factor startsincreasing. However, even with the increase, the Y-phase hexagonalferrite material maintains a loss factor of about 2 at 1 GHz.

Further, while maintaining the low loss factor, the material shown inFIG. 9 also contains a permeability of greater than 4, from about 4-5,which is over double that of standard Y-phase hexagonal ferritematerials. Moreover, it is noticeable that there is a large spike inpermeability at around 1 GHz, where permeability increases to about 6.Therefore, at 1 GHz, embodiments of the material have a largepermeability while still maintaining the relatively low loss factor.

Accordingly, because of the low loss factor and the high magneticpermeability, embodiments of the Y-phase hexagonal ferrite materialshown with respect to FIG. 9 can be advantageous for use as amagnetodielectric material, such as in a radio frequency antenna orother high frequency applications.

Substitution with Sodium (Na)

While the disclosure above shows one method for improving the magneticproperties of a Y-phase hexagonal ferrite materials, differentimprovements can be made into the hexagonal ferrite material bysubstituting sodium into the crystal structure of the Y-phase hexagonalferrite material. This incorporation can be done with, or without, theother methods for improving magnetic properties discussed throughout theapplication.

In order to increase the resonant frequency of a material, such as theY-phase hexagonal ferrite, small amounts of alkali metals can be dopedinto the composition. For example, lithium, sodium, potassium, andrubidium can all be doped into the hexagonal ferrite. In doing so,strontium atoms can be substituted out to make room for the alkalimetals. This addition of alkali metal, can prevent the reduction of ironto the Fe²⁺ state. Since the alkali metal with a 1+ oxidation statesubstitutes for Sr with a 2+ oxidation state, it decreases thelikelihood of Fe³⁺ converting to Fe²⁺ because, in this case, the averagemetal oxidation state becomes too low. Therefore, the reduction of ironduring sintering is inhibited. By avoiding the reduction of iron, thethreshold for the resonant frequency can be pushed higher than valuesthat have been previously obtained. Fe²⁺ decreases the resonantfrequency and contributes to both the magnetic and the dielectric losstangents. Accordingly, the increased resonant frequency, along with thedecreased magnetic loss tangent, can then result in a correspondingincrease in the magnetic Q factor, allowing for embodiments of thedisclosed material to have advantageous uses as a magnetodielectricmaterial.

In some embodiments, sodium (Na) can be used as an atom to substituteinto the crystal structure of the Y-phase strontium hexagonal ferrite.By incorporating sodium into the crystal structure, high magneticpermeability values can be achieved while maintaining high Q values,thus improving embodiments of the material for use as amagnetodielectric material.

In some embodiments, Na⁺ can be used to substitute out some of the Sr²⁺atoms in the Y-phase hexagonal ferrite. The substitution can beperformed through numerous methods, and can include numerouscompositions having sodium, and the method of substitution is notlimiting. For example, in some embodiments the substitution of strontiumfor sodium can be performed without charge compensation elsewhere in thelattice or with charge compensation through a coupled substitution inthe Sr—Co—Y lattice.

However, strontium and sodium have different charges to their atoms, 2for strontium and 1 for sodium, and thus some charge balancing can beused to avoid significant distortion of any crystal structure. In someembodiments, a trivalent or tetravalent species can be substituted infor cobalt (having a 2+ charge, similar to strontium), which cancompensate for the charge imbalance that occurs by substituting Na⁺ infor Sr²⁺, thus leading to a generally balanced chemical structure. Dueto the ability to provide charge balancing, two series of compounds canbe used, one for trivalent ion substitutions of cobalt and one fortetravalent ion substitutions of cobalt.

For trivalent ion substitution, the below example composition can beused:

Sr_(2-x)Na_(x)Co_(2-x)M_(x)Fe₁₂O₂₂

where M is a trivalent cation such as Al, Ga, Sc, Cr, Mn, In, Yb, Er, Yor other lanthanide, though the trivalent ion is not limiting. Further,x values can be in the range of about 0 to about 1.5. In someembodiments, 0.2<x<0.7.

For tetravalent ion substitution, the below equation can be used:

Sr_(2-2x)Na_(2x)Co_(2x)N_(x)Fe₁₂O₂₂

where N can be Si, Ge, Ti, Zr, Sn, Ce, Pr, Hf, or Tb, though thetetravalent ion is not limiting. Further, x values can be in the rangeof about 0 to about 1.5. In some embodiments, 0.2<x<0.7. In someembodiments where x=0.4, very high permeability values at low loss arealso observed.

FIGS. 10-11 show impedance spectra using the above disclosedsubstitution technique. Typically, the impedance spectra is performedusing dielectric spectroscopy, also known as impedance spectroscopy orelectrochemical impedance spectroscopy. The impedance spectra canadvantageously show the different dielectric properties of a medium as afunction of different frequencies.

In FIGS. 10-11, the impedance spectra shows both permeability (μ′) aswell as loss factor (μ″) across a range of frequencies. It can beadvantageous for radio frequency applications to have minimal movementacross the range of frequencies, which shows that there is minimal lossat those particular frequencies. When the loss factor begins to spike,the material may experience more loss during use at those frequencies.At a certain point, the material may become unusable for antennaapplications at that particular range of frequencies due to the highloss.

Along with minimizing the loss factor spike, it can be advantageous toadjust the spike in loss factor as far towards the high range offrequency as possible. As mentioned, when the loss factor spikes, thematerial may become less useful in those particular frequencies. Sohaving a loss factor spike at higher frequencies can generally mean thatthe material can be used at higher frequencies with minimized loss.

FIG. 10 illustrates the permeability and loss factor for a hexagonalferrite material using Sc where x=0.25. Accordingly, the generalequation is Sr_(1.75)Na_(0.25)Co_(1.75)Sc_(0.25)Fe₁₂O₂₂.

As shown in FIG. 10, the loss factor of an embodiment of the Y-phasehexagonal ferrite material does not rise above 4 until 1 GHz. In fact,the loss factor of the hexagonal ferrite material remains relativelyconstant at around 3 up through approximately 800 MHz.

While maintaining the low loss factor, the material shown in FIG. 10also maintains a permeability of around 5. This is over double thepermeability that is found in typical Y-phase hexagonal ferritematerials.

Accordingly, because of the low loss factor and the high magneticpermeability, embodiments of the Y-phase hexagonal ferrite materialshown with respect to FIG. 10 can be advantageous for use as amagnetodielectric material, such as in a radiofrequency antenna.

FIG. 11 illustrates the permeability and loss factor for a hexagonalferrite material using Sc where x=0.5. Accordingly, the general equationis Sr_(1.5)Na_(0.5)Co_(1.5)Sc_(0.5)Fe₁₂O₂₂.

As shown in FIG. 11, the loss factor of an embodiment of the Y-phasehexagonal ferrite material does not rise above 4 until well above 1 GHz.In fact, the loss factor of the hexagonal ferrite material remainsrelatively constant just below 3 up through approximately 800 MHz. Evenat a frequency of 1 GHz, the material only has a loss factor of around3. Accordingly, embodiments of this disclosed Y-phase hexagonal ferritematerial are particularly suited for high resonant frequency antennaapplications.

Additionally, while maintaining the low loss factor, the material shownin FIG. 11 also maintains a permeability of about 5 to about 6. This isover double to about triple the permeability that is found in typicalY-phase hexagonal ferrite materials.

Accordingly, because of the low loss factor and the high magneticpermeability, embodiments of the Y-phase hexagonal ferrite materialshown with respect to FIG. 11 can be advantageous for use as amagnetodielectric material, such as in a radiofrequency antenna.

Processing

FIGS. 12-16 illustrate processes for fabricating ferrite devices, suchas radio frequency antennas, using one or more of the embodiments of theabove disclosed hexagonal ferrite materials and having one or morefeatures as described herein. FIG. 12 shows a process 20 that can beimplemented to fabricate a ceramic material having one or more of theforegoing properties. In block 21, powder can be prepared. In block 22,a shaped object can be formed from the prepared powder. In block 23, theformed object can be sintered. In block 24, the sintered object can befinished to yield a finished ceramic object having one or more desirableproperties.

In implementations where the finished ceramic object is part of adevice, the device can be assembled in block 25. In implementationswhere the device or the finished ceramic object is part of a product,the product can be assembled in block 26.

FIG. 12 further shows that some or all of the steps of the exampleprocess 20 can be based on a design, specification, etc. Similarly, someor all of the steps can include or be subjected to testing, qualitycontrol, etc.

Powder prepared can include one or more properties as described herein,and/or facilitate formation of ceramic objects having one or moreproperties as described herein.

In some implementations, powder prepared as described herein can beformed into different shapes by different forming techniques. By way ofexamples, FIG. 13 shows a process 50 that can be implemented topress-form a shaped object from a powder material prepared as describedherein. In block 52, a shaped die can be filled with a desired amount ofthe powder. In FIG. 14, configuration 60 shows the shaped die as 61 thatdefines a volume 62 dimensioned to receive the powder 63 and allow suchpower to be pressed. In block 53, the powder in the die can becompressed to form a shaped object. Configuration 64 shows the powder inan intermediate compacted form 67 as a piston 65 is pressed (arrow 66)into the volume 62 defined by the die 61. In block 54, pressure can beremoved from the die. In block 55, the piston (65) can be removed fromthe die (61) so as to open the volume (62). Configuration 68 shows theopened volume (62) of the die (61) thereby allowing the formed object 69to be removed from the die. In block 56, the formed object (69) can beremoved from the die (61). In block 57, the formed object can be storedfor further processing. Additional forming methods familiar to thoseskilled in the art include but are not limited to isostatic pressing,tape casting, tape calendaring and extrusion

In some implementations, formed objects fabricated as described hereincan be sintered to yield desirable physical properties as ceramicdevices. FIG. 15 shows a process 70 that can be implemented to sintersuch formed objects. In block 71, formed objects can be provided. Inblock 72, the formed objects can be introduced into a kiln. In FIG. 16,a plurality of formed objects 69 are shown to be loaded into a sinteringtray 80. The example tray 80 is shown to define a recess 83 dimensionedto hold the formed objects 69 on a surface 82 so that the upper edge ofthe tray is higher than the upper portions of the formed objects 69.Such a configuration allows the loaded trays to be stacked during thesintering process. The example tray 80 is further shown to definecutouts 83 at the side walls to allow improved circulation of hot gas atwithin the recess 83, even when the trays are stacked together. FIG. 16further shows a stack 84 of a plurality of loaded trays 80. A top cover85 can be provided so that the objects loaded in the top tray generallyexperience similar sintering condition as those in lower trays.

In block 73, heat can be applied to the formed objects so as to yieldsintered objects, such as antennas. Such application of heat can beachieved by use of a kiln. In block 74, the sintered objects can beremoved from the kiln. In FIG. 16, the stack 84 having a plurality ofloaded trays is depicted as being introduced into a kiln 87 (stage 86a). Such a stack can be moved through the kiln (stages 86 b, 86 c) basedon a desired time and temperature profile. In stage 86 d, the stack 84is depicted as being removed from the kiln so as to be cooled.

In block 75, the sintered objects can be cooled. Such cooling can bebased on a desired time and temperature profile. In block 206, thecooled objects can undergo one or more finishing operations. In block207, one or more tests can be performed.

Heat treatment of various forms of powder and various forms of shapedobjects are described herein as calcining, firing, annealing, and/orsintering. It will be understood that such terms may be usedinterchangeably in some appropriate situations, in context-specificmanners, or some combination thereof.

Substitution of Scandium, Silicon, and/or Manganese

For magnetodielectric antenna applications, it can be advantageous tohave as high of a magnetic permeability as possible. Having highmagnetic permeability can lead to many benefits for magnetodielectricapplications, such as improved miniaturization factors, thus leading tosmaller overall footprints of components, and impedance matching to freespace. Further, it can be advantageous to have high resonant frequencieswhich can maximize the operating frequencies of the electronic devicesthat the material is incorporated into, thus allowing for use of theelectronic devices in higher frequency arenas.

However, high permeability magnetic oxides which have typically beenused for antenna applications in the prior art tend to have lowresonance frequencies. The few materials that do have high resonancefrequencies usually have low magnetic permeability, making themunsuitable for use in high frequency magnetodielectric applications. Forexample, Sr₂Co₂Fe₁₂O₂₂ (Sr—Co—Y phase) has a resonant frequency wellabove 1 GHz, but a permeability of only 2. Thus, prior art materialshave not been usable to efficiently handle high frequency applications.

Previous solutions have been focused on increasing the resonantfrequency of Z-phase hexagonal ferrite material (e.g. Co₂ZBa₃Co₂Fe₂₄O₄₁). Specifically, substitutions of alkali metals for thebarium ion in Co₂Z have been performed, as disclosed in U.S. Pat. Nos.8,524,190 and 8,609,062, hereby incorporated by reference in theirentirety. While the incorporation of alkali metals for the barium hasincreased the resonant frequency of the material, the useable frequencyof the material may still be lower than desired. So while modestimprovements in resonant frequency have been detailed in the abovedisclosure, they may not have significantly extended the useablefrequency range for Co₂Z materials.

Accordingly, disclosed herein are embodiments of a Y-phase strontiumhexagonal ferrite material (Co₂Y), as discussed above, that can haveboth high magnetic permeability as well as high resonance frequencies,thus making the material advantageous for use in high frequency antennaapplications.

In some embodiments, permeability can be doubled or tripled from thetypical values using coupled substation of an Sr—Co—Y phase hexagonalferrite material. Further, the resonant frequency of the Y-phasehexagonal ferrite materials, relative to the Z-phase materials, canincrease into the range of about 500 MHz to about 1 GHz, allowing forthe material to be used for high frequency applications.

In some embodiments, as mentioned above, an example Y-phase hexagonalferrite that can be used for high dielectric antenna components can havethe equation:

Sr_(2-x)K_(x)Co_(2-x)M_(x)Fe₁₂O₂₂ or Sr_(2-x)Na_(x)Co_(2-x)M_(x)Fe₁₂O₂₂

when M is scandium or indium (Sc³⁺ or In³⁺). When scandium or indium issubstituted for cobalt, this can lead to increased magneticpermeability. Most likely, this occurs because the cobalt, scandium, andindium all have a relatively similar ionic size according to theShannon-Prewitt effective ionic radius. For example, cobalt has an ionicsize of 0.885 angstroms while scandium and indium have ionic sizes of0.885 and 0.94, respectively. In fact, the scandium and cobalt havealmost identical sizes. Accordingly, when these elements are substitutedinto the crystal structure of the Co₂Y material, minimal deformation tothe crystal structure is likely to occur due to the replacement atomsfitting in generally the same place as the original atom.

Following the above equation, in some embodiments silica and/or aluminumcan further be incorporated into a Sr—Co—Y or the Sc and Naco-substituted hexagonal ferrite material, thereby generally increasingthe resonant frequency and permeability of the hexagonal ferritematerial, providing for advantageous properties for radiofrequencycomponents. For example, in some embodiments, Al³⁺ can be substituted infor Fe³⁺, thereby adjusting the Sr₂Co₂Fe₁₂O₂₂ lattice to include thesubstituted atoms.

Thus, in some embodiments, the composition can beSr₂Co₂Fe_(12-y)Al_(y)O₂₂ orSr_(2-x)(K,Na)_(x)Co_(2-x)M_(x)Fe_(12-y)Al_(y)O₂₂ where M is scandium orindium (Sc³⁺ or In³⁺).

Further, silicon can be added into the Sr₂Co₂Fe₁₂O₂₂,Sr_(2-x)(K,Na)_(x)Co_(2-x) M_(x)Fe₁₂O₂₂ orSr_(2-x)(K,Na)_(x)Co_(2-x)M_(x)Fe_(12-y)Al_(y)O₂₂ where M is scandium orindium (Sc³⁺ or In³⁺) to adjust the magnetic properties of the hexagonalferrite material. Si additions can act as a grain growth inhibitor andtherefore be segregated at the grain boundaries, which can reducemagnetorestriction effects in sintered materials.

Moreover, Mn³⁺ can be added into the hexagonal ferrite material toprevent Fe³⁺ reduction as discussed above, and thus improve thedielectric loss.

In some embodiments, silicon can be located in the grain boundaries ofthe crystal structure, while manganese and aluminum can be incorporatedinto the crystal structure, those this configuration is not limiting.

In some embodiments, the composition can be Sr₂Co₂Fe_(12-y)Mn_(y)O₂₂,Sr_(2-x)K_(x)Co_(2-x)M_(x)Fe_(12-y)Mn_(y)O₂₂ orSr_(2-x)K_(x)Co_(2-x)M_(x)Fe_(12-y-z)Mn_(y)Al_(z)O₂₂ where M is scandiumor indium (Sc³⁺ or In³⁺).

FIGS. 1 and 17 show impedance spectra using the above disclosedsubstitution technique. Typically, the impedance spectra is performedusing dielectric spectroscopy, also known as impedance spectroscopy orelectrochemical impedance spectroscopy. The impedance spectra can showthe different dielectric properties of a medium as a function ofdifferent frequencies. Specifically, FIGS. 1 and 17 illustrates twodifferent compositions of a Y-phase hexagonal ferrite including Sc, Al,Si, and Mn.

In FIGS. 1 and 17, the impedance spectra shows both permeability (μ′) aswell as loss factor (μ″) across a range of frequencies. It can beadvantageous for magnetodielectric materials used in radio frequencyapplications to have a minimal change in properties across the range offrequencies, and in particular a minimal μ″ and therefore a minimal losstangent at those particular frequencies. When the loss tangent begins toincrease or spike, the material would become unsuitable for antennaapplications.

Along with minimizing the loss tangent spike, it can be advantageous toadjust the spike in loss tangent to as high a frequency as possible. Asmentioned, when the loss tangent spikes, the material becomes lessuseful at that frequency. So having a loss tangent spike at higherfrequencies means that the material can be used at higher frequencieswith minimized loss.

FIG. 1 shows an embodiment of the above composition where x=0.3 andincluding Sc, thus formingSr_(1.7)Na_(0.3)Co_(1.7)Sc_(0.3)Fe_(11.5)Al_(0.5)O₂₂. As shown, the losstangent of the composition can be relatively minimized until higherresonant frequency spectrums. For example, the permeability and lossfactor of the material is approximately 5 up through over 500 MHz. Whileat this point the μ″ (loss factor) and the loss tangent begins tosteadily increase, the low μ″ and loss tangent is retained even up to 1GHz. This is a high permeability and low loss factor for such highfrequencies, and shows that embodiments of the disclosed material isadvantageous for high frequency applications.

FIG. 17 shows an embodiment of the above composition where x=0.4 andincluding Sc, thus formingSr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe_(11.5)Al_(0.5)O₂₂. As shown, the losstangent of the composition can be relatively minimized until higherresonant frequency spectrums. For example, the permeability of thematerial is approximately 5 up through over 500 MHz whereas the lossfactor is approximately 6. While at this point the μ″ (loss factor) andthe loss tangent begins to steadily increase, the low μ″ and losstangent is retained even up to 1 GHz. This is a high permeability andlow loss factor for such high frequencies, and shows that embodiments ofthe disclosed material is advantageous for high frequency applications.

Incorporation of Stoichiometric Oxides

While the disclosure above shows certain methods and substitutions forimproving the magnetic properties of a Y-phase hexagonal ferritematerials, improvements can also be made into the hexagonal ferritematerial by incorporating second-phase oxides into the hexagonal ferritematerial. These second-phase oxides can either dissolve into the mainhexagonal phase structure, making it non-stoichiometric, or may beincorporated into the ceramic as second phases. This incorporation canbe done with, or without, the other methods for improving magneticproperties disclosed otherwise herein.

Thus, in some embodiments, oxides consistent with the stoichiometry ofZ-Phase Sr₃Co₂Fe₂₄O₄₁ could be incorporated into embodiments of aY-phase hexagonal ferrite material to improve certain magneticproperties of the material. Additionally, CoFe₂O₄ (with the spinelstructure) or SrFe₁₂O₁₉ (with the magnetoplumbite structure) can beadded to the Y-phase hexagonal ferrite material and may either dissolvein the Y-phase making it non-stoichiometric or exist as distinct secondphases within the ceramic body. However, other oxides can be used aswell and the specific oxide incorporated into the material is notlimiting.

In some embodiments, the oxides can be incorporated into a specificY-phase hexagonal ferrite composition. For example, these compounds canbe incorporated into a structure ofSr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₁O₂₂ to form a hexagonal ferritematerial having improved properties. However, other compositions ofY-phase hexagonal ferrite can be used, and the type of Y-phase hexagonalferrite in which the oxide is incorporated into is not limiting. Theincluded oxide additions can be advantageous as they can improve atleast some of the magnetodielectric properties discussed above. Further,by the improving magnetic properties, a number of compositions which canbe used to synthesize magnetodielectric antenna materials can be used.

In some embodiments, a combination ofSr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₁O₂₂ with 2 (or about 2) wt. %Sr₃Co₂Fe₂₄O₄₁ can lead to excellent properties for use as amagnetodielectric antenna material. For example, FIG. 18 shows Mu′(permeability) and magnetic Q data compared to a frequency applied tothe hexagonal ferrite material.

As shown in FIG. 18, the Q factor of an embodiment of the disclosedY-phase hexagonal ferrite material is extremely high at low frequencyvalues. However, it is advantageous for the material to maintain high Qfactor values even at higher frequencies, such as those between 500 MHzand 1 GHz or above. Advantageously, embodiments of the disclosedmaterial are able to maintain relatively high Q factors even at thesehigh frequencies. While Q values do decrease as the applied frequencyincreases, the drop is not drastic, which would occur in other materialspreviously used. Accordingly, embodiments of the disclosed hexagonalferrite material still maintain/achieve high Q values at highfrequencies.

For example, embodiments of the hexagonal ferrite material have a Qvalue of greater than about 20 at 800 MHz. Further, embodiments of thehexagonal ferrite material have a Q value of greater than about 15 at 1GHz. Therefore, embodiments of the disclosed Y-phase hexagonal ferritematerial can be used in higher frequency applications than are possiblewith current bulk materials.

Moreover, as shown in FIG. 18, the hexagonal ferrite material canmaintain a high permeability throughout its frequency ranges even whilehaving the high Q factor discussed above. As shown, the hexagonalferrite material maintains a relatively even permeability, μ′ of about6, 7, or 8 through 800 MHz to 1 GHz. This permeability level issignificantly higher than the typical permeability value of 2 for abasic Y-phase hexagonal ferrite structure. In fact, embodiments of thedisclosed Y-phase hexagonal ferrite values can achieve permeabilitylevels of 2 to 3 times that of standard Y-phase hexagonal ferritematerials at high frequencies. Accordingly, embodiments of the disclosedhexagonal ferrite material can achieve high Q values while alsomaintaining high permeability, thus making them advantageous for use inmagnetodielectric antennas at frequencies between 500 MHz and 1 GHz.

Further, embodiments of the hexagonal ferrite material can have adielectric constant (e.g., permittivity) of approximately 10-11. Therelatively high permeability gives these materials a better impedancematch to free space than Sr₂Co₂Fe₁₂O₂₂. Recall that when μ_(r)=ε_(r),there is a perfect impedance match to free space.

Two figures of merit for antenna performance include the miniaturizationfactor and the bandwidth. First, the miniaturization factor isdetermined by the formula:

d _(eff) =d _(o)(ε_(r)μ_(r))^(−1/2)

where d_(eff)/d_(o) are the miniaturization factor, ε_(r) is thedielectric constant of the antenna material, and μ_(r) is the magneticpermeability of the antenna material. Both ε_(r) and μ_(r) are dependenton frequency in magnetic oxide antennas. Second the effective bandwidth(or efficiency) is determined by the formula:

η=η_(o)(μ_(r)/ε_(r))^(1/2)

where η/η_(o) describes the efficiency (or bandwidth) of the material.This efficiency is maximized if μ_(r) is maximized.

It can be advantageous for miniaturization to have both high dielectricconstant and high permeability. Having high values can lead to improvedminiaturization factors. Further, for the efficiency equation, it can beadvantageous to have permeability greater to or equal to that of thedielectric constant. However, it can be advantageous to have bothpermeability and dielectric constant to be as high as possible.Accordingly, because embodiments of the described Y-phase hexagonalferrite material have high permeability and high dielectric constant,and having a dielectric constant relatively close to permeability, theycan be useful for antenna applications where a good impedance match tofree space is desirable.

Table I illustrates magnetic permeability spectra of embodiments ofsubstituted Sr—Co—Y phase hexagonal ferrites, such as using the methodsdescribed in detail above.

TABLE I Magnetic Permeability Spectra 500 500 500 750 750 750 1 1 1Sample (all added MHz MHz MHz MHz MHz MHz GHz GHz GHz percents byweight) μ′ μ″ Q μ′ μ″ Q μ′ μ″ Q Sr₂Co₂Fe₁₂O₂₂ 2.34 .108 21.7 2.35 .14516.2 2.37 .190 12.5 Sr₂Co₂Fe₁₂O₂₂ + 0.1% K₂CO₃ 2.47 .050 49.4 2.53 .07235.1 2.60 .091 28.6 Sr_(1.75)K_(0.25)Co_(1.75)Sc_(0.25)Fe₁₂O₂₂ 3.82 .16722.9 3.93 .242 16.2 4.10 .359 11.4Sr_(1.5)K_(0.5)Co_(1.5)Sc_(0.5)Fe₁₂O₂₂ 3.28 .148 22.2 3.42 .233 14.73.63 .411 8.83 Sr_(1.75)K_(0.25)Co_(1.75)In_(0.25)Fe₁₂O₂₂ 3.08 .138 22.33.19 .188 17.0 3.37 .298 11.3 Sr_(1.5)K_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂4.64 .204 22.7 5.21 .540 9.65 5.92 1.61 3.68Sr_(1.75)Na._(0.25)Co_(1.75)Sc_(0.25)Fe₁₂ 5.12 .181 28.3 5.31 .285 18.65.66 .421 13.4 O₂₂ Sr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₂O₂₂ 6.12 .22727.0 6.42 .356 18.0 6.92 .531 13.0Sr_(1.5)Na_(0.5)Co_(1.5)Sc_(0.5)Fe₁₂O₂₂ 5.23 .179 29.2 5.44 .266 20.55.91 .401 14.7 Sr_(1.75)Na_(0.25)Co_(1.75)In_(0.25)Fe₁₂O₂₂ 1.67 .03449.1 1.68 .046 36.5 1.70 .056 30.4Sr_(1.5)Na_(0.5)Co_(1.5)In_(0.5)Fe₁₂O₂₂ 1.83 .025 73.2 1.83 .056 32.71.85 .064 28.9 Sr_(1.7)Na_(0.3)Co_(1.7)Sc_(0.3)Fe₁₂O₂₂ + 4.81 .198 24.35.05 .401 12.6 5.35 .711 7.52 0.5% Al₂O₃, 0.2% MnO₂ and 0.2% SiO₂Sr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₂O₂₂ + 5.11 .183 27.9 5.48 .482 11.45.74 1.04 5.52 0.5% Al₂O₃, 0.2% MnO₂ and 0.2% SiO₂Sr_(1.6)Na_(0.4)Co_(1.6)Sc_(0.4)Fe₁₂O₂₂ + 6.17 .185 33.4 6.47 .275 23.56.95 .442 15.72 2.0% Sr₃CO₂Fe₂₄O₄₁

Processing

Certain aspects of the present disclosure provide processing techniquesfor increasing the permeability of Y phase hexaferrites at higherfrequencies. In one implementation, the processing techniques involvemethods of magnetic texturing of Y phase hexaferrites to result in atextured ceramic with improved magnetic properties. In one embodiment,the method of magnetic texturing used in forming involves using areaction sintering method, which includes the steps of aligning M-phase(BaFe₁₂O₁₉ uniaxial magnetization) with non-magnetic additives in astatic magnetic field and reacting with BaO source and CoO to form theY-phase (Sr₂Me₂Fe₁₂O₂₂). In another embodiment, the method of magnetictexturing used in forming Sr—Co₂Y involves using a rotating magneticfield method, which includes the steps of aligning Sr—Co₂Y phase (planarmagnetization) with magnetic texturing occurring in a rotating magneticfield. The inventor has found that the degree of alignment, thuspermeability gain, is far superior in a rotating magnetic field.

In some embodiments, the processing technique for forming the Y phasematerial includes making Y phase Fe deficient to inhibit reduction of Feas the inventor believes that dielectric and magnetic loss is increasedby reduction of Fe (Fe³⁺→Fe²⁺) at high temperatures. The processingtechnique includes the step of heat treatment or annealing in oxygen toinhibit reduction of Fe and cause Fe²⁺→Fe³.

In some other embodiments, the processing technique for forming Sr—Co₂Yincludes forming fine grain hexagonal ferrite particles. The processinvolves using high energy milling to reduce the particle size.

FIG. 19 illustrates a method 100 of forming a Sr—Co₂Y material accordingto a preferred embodiment. As shown in FIG. 19, appropriate amounts ofprecursor materials—reactants that may provide strontium, cobalt, iron,one or more alkali metals, scandium, indium, aluminum, silica, manganeseand oxygen that can form the magnetic material—are mixed together inStep 102. In some aspects, at least a portion of the oxygen may beprovided in the form of an oxygen-containing compound of strontium (Sr),cobalt (Co), iron (Fe), or one or more alkali metals. For example, theseelements may be provided in carbonate or oxide forms, or in otheroxygen-containing precursor forms known in the art. In one or moreaspects, one or more precursor materials may be provided in anon-oxygen-containing compound, or in a pure elemental form. In otheraspects, oxygen could be supplied from a separate compound, such as, forexample, H₂O₂ or from gaseous oxygen or air. For example, in oneembodiment, SrCO₃, Co₃O₄, NaHCO₃, Sc₂O₃ and Fe₂O₃ precursors are mixedin a ratio appropriate for the formation of the Y phase material. Theseprecursor compounds may be mixed or blended in water or alcohol using,for example, a Cowles mixer, a ball mill, or a vibratory mill. Theseprecursors may also be blended in a dry form.

The blended mixture may then be dried if necessary in Step 104. Themixture may be dried in any of a number of ways, including, for example,pan drying or spray drying. The dried mixture may then be heated in Step106 at a temperature and for a period of time to promote calcination.For example, the temperature in the heating system used in heating Step106 may increase at a rate of between about 20° C. per hour and about200° C. per hour to achieve a soak temperature of about 1000° C.-1300°C., or about 1100° C. to 1250° C., which may be maintained for about twohours to about twelve hours. The heating system may be, for example, anoven or a kiln. The mixture may experience a loss of moisture, and/orreduction or oxidation of one or more components, and/or thedecomposition of carbonates and/or organic compounds which may bepresent. At least a portion of the mixture may form a hexaferrite solidsolution

The temperature ramp rate, the soak temperature, and the time for whichthe mixture is heated may be chosen depending on the requirements for aparticular application. For example, if small crystal grains are desiredin the material after heating, a faster temperature ramp, and/or lowersoak temperature, and/or shorter heating time may be selected as opposedto an application where larger crystal grains are desired. In addition,the use of different amounts and/or forms of precursor materials mayresult in different requirements for parameters such as temperature ramprate and soaking temperature and/or time to provide desiredcharacteristics to the post-heated mixture.

After heating, the mixture, which may have formed agglomerated particlesof hexaferrite solid solution, may be cooled to room temperature, or toany other temperature that would facilitate further processing. Thecooling rate of the heating system may be, for example, 80° C. per hour.In step 108, the agglomerated particles may be milled. Milling may takeplace in water, in alcohol, in a ball mill, a vibratory mill, or othermilling apparatus. In some embodiments, the milling is continued untilthe median particle diameter of the resulting powdered material is fromabout one to about four microns, although other particle sizes, forexample, from about one to about ten microns in diameter, may beacceptable in some applications. In a preferred embodiment, high energymilling is used to mill the particles to a fine particle size of 0.2 to0.9 microns in diameter. This particle size may be measured using, forexample, a sedigraph or a laser scattering technique. A target medianparticle size may be selected to provide sufficient surface area of theparticles to facilitate sintering in a later step. Particles with asmaller median diameter may be more reactive and more easily sinteredthan larger particles. In some methods, one or more alkali metals oralkali metal precursors or other dopant materials may be added at thispoint rather than, or in addition to, in step 102.

The powdered material may be dried if necessary in step 110 and thedried powder may be pressed into a desired shape using, for example, auniaxial press or an isostatic press in step 112. The pressure used topress the material may be, for example, up to 80,000 N/m, and istypically in the range of from about 20,000 N/m to about 60,000N/m.sup.2. A higher pressing pressure may result in a more densematerial subsequent to further heating than a lower pressing pressure.

In step 114, the pressed powdered material may be sintered to form asolid mass of doped hexaferrite. The solid mass of doped hexaferrite maybe sintered in a mold having the shape of a component desired to beformed from the doped hexaferrite. Sintering of the doped hexaferritemay be performed at a suitable or desired temperature and for a timeperiod sufficient to provide one or more desired characteristics, suchas, but not limited to, crystal grain size, level of impurities,compressibility, tensile strength, porosity, and in some cases, magneticpermeability. Preferably, the sintering conditions promote one or moredesired material characteristics without affecting, or at least withacceptable changes to other undesirable properties. For example, thesintering conditions may promote formation of the sintered dopedhexaferrite with little or minimal iron reduction. In one embodiment,the temperature used in the sintering step 114 is preferably between1100° C. to 1250° C. According to some embodiments, the temperature inthe heating system used in the sintering step 114 may be increased at arate of between about 20° C. per hour and about 200° C. per hour toachieve a soak temperature of about 1000° C.-1450° C. or about 1100° C.to 1150° C. or about 1100° C.-1250° C. which may be maintained for abouttwo hours to about twelve hours. The heating system may be, for example,an oven or a kiln. A slower ramp, and/or higher soak temperature, and/orlonger sintering time may result in a more dense sintered material thanmight be achieved using a faster temperature ramp, and/or lower soaktemperature, and/or shorter heating time. Increasing the density of thefinal sintered material by making adjustments, for example, to thesintering process can be performed to provide a material with a desiredmagnetic permeability, saturation magnetization, and/ormagnetorestriction coefficient. According to some embodiments of methodsaccording to the present disclosure, the density range of the sinteredhexaferrite may be between about 4.50 g/cm³ and about 5.36 g/cm³. Adesired magnetic permeability of the doped hexaferrite may also beachieved by tailoring the heat treatment of the material to producegrains with desired sizes. The hexaferrite may also be crush pressed andfurther sintered in step 116 to form a final hexaferrite product.

The grain size of material produced by embodiments of the above methodmay vary from between about five micrometers and one millimeter indiameter depending upon the processing conditions, with even largergrain sizes possible in some aspects of methods according to the presentdisclosure. In some aspects, each crystal of the material may comprise asingle magnetic domain. Both doped Sr—Co₂Y and chemically substituted(for example, Na and Sc) Sr—Co₂Y may be members of the planarhexaferrite family called ferroxplana, having a Y-type ferrite crystalstructure.

FIG. 20 illustrates a method 200 of forming textured Sr—Co₂Y accordingto another embodiment adapted to reduce the magnetorestriction andimprove the resonant frequency of the material. The method 200 beginswith step 202 in which a fine grain hexagonal ferrite powder is formed.In one implementation, the fine grain hexagonal ferrite powder is astrontium cobalt ferrite Y-phase powder. This powder can be synthesizedusing a chemical process known in the art such as co-precipitation. TheSr—Co₂Y can also be synthesized via sol-gel, calcining, and mechanicalmilling using a Netzsch zeta-mill or the like. In one embodiment, theSr—Co₂Y powder has particle sizes of less than about 1 micron andsurface areas of greater than about 6 m²/g. In another embodiment, theSr—Co₂Y powder has an average particle size of less than about 1 micronand an average surface area of greater than about 6 m²/g.

As FIG. 20 further shows, the method 200 further comprises step 204 inwhich the hexagonal ferrite powder is compacted by a known process suchas cold isostatic pressing, uniaxial pressing, extrusion, or the like.As also shown in FIG. 20, the hexagonal powder is subsequently fired atstep 206 at a temperature between about 1100° C. to 1250° C., which islower than the standard, conventional sintering temperature for the samematerial. The resulting material is preferably a fine grained hexagonalferrite material.

Power Amplifier Modules and Wireless Devices

FIGS. 21 and 22 respectively illustrate a power amplifier module 10 andwireless device 11 which can include one or more radio frequency devicesimplemented using any of the methods, materials, and devices of thepresent disclosure. For instance, the power amplifier module 10 and thewireless device 11 can include one or more antennas, transformers,inductors, circulators, absorbers, or other RF devices or other devicesimplemented according to the present disclosure, including devicesincorporating, without limitation: increased resonant frequencyalkali-doped y-phase hexagonal ferrites, increased resonant frequencypotassium-doped hexagonal ferrite, magnetodielectric y-phase strontiumhexagonal ferrite materials formed by sodium substitution, and ferritematerial incorporating oxides for radiofrequency operations.

FIG. 21 is a schematic diagram of a power amplifier module (PAM) 10 foramplifying a radio frequency (RF) signal. The illustrated poweramplifier module 10 amplifies an RF signal (RF_IN) to generate anamplified RF signal (RF_OUT).

FIG. 22 is a schematic block diagram of an example wireless or mobiledevice 11. The example wireless device 11 depicted in FIG. 22 canrepresent a multi-band and/or multi-mode device such as amulti-band/multi-mode mobile phone. By way of examples, Global Systemfor Mobile (GSM) communication standard is a mode of digital cellularcommunication that is utilized in many parts of the world. GSM modemobile phones can operate at one or more of four frequency bands: 850MHz (approximately 824-849 MHz for Tx, 869-894 MHz for Rx), 900 MHz(approximately 880-915 MHz for Tx, 925-960 MHz for Rx), 1800 MHz(approximately 1710-1785 MHz for Tx, 1805-1880 MHz for Rx), and 1900 MHz(approximately 1850-1910 MHz for Tx, 1930-1990 MHz for Rx). Variationsand/or regional/national implementations of the GSM bands are alsoutilized in different parts of the world.

Code division multiple access (CDMA) is another standard that can beimplemented in mobile phone devices. In certain implementations, CDMAdevices can operate in one or more of 800 MHz, 900 MHz, 1800 MHz and1900 MHz bands, while certain W-CDMA and Long Term Evolution (LTE)devices can operate over, for example, 22 or more radio frequencyspectrum bands.

One or more features of the present disclosure can be implemented in theforegoing example modes and/or bands, and in other communicationstandards. For example, 802.11, 2G, 3G, 4G, LTE, and Advanced LTE arenon-limiting examples of such standards. To increase data rates, thewireless device 11 can operate using complex modulated signals, such as64 QAM signals.

In certain embodiments, the wireless device 11 can include switches 12,a transceiver 13, an antenna 14, power amplifiers 17 a, 17 b, a controlcomponent 18, a computer readable medium 19, a processor 20, a battery21, and a power management system 30, any of which can includeembodiments of the disclosed material.

The transceiver 13 can generate RF signals for transmission via theantenna 14. Furthermore, the transceiver 13 can receive incoming RFsignals from the antenna 14.

It will be understood that various functionalities associated with thetransmission and receiving of RF signals can be achieved by one or morecomponents that are collectively represented in FIG. 22 as thetransceiver 13. For example, a single component can be configured toprovide both transmitting and receiving functionalities. In anotherexample, transmitting and receiving functionalities can be provided byseparate components.

Similarly, it will be understood that various antenna functionalitiesassociated with the transmission and receiving of RF signals can beachieved by one or more components that are collectively represented inFIG. 22 as the antenna 14. For example, a single antenna can beconfigured to provide both transmitting and receiving functionalities.In another example, transmitting and receiving functionalities can beprovided by separate antennas. In yet another example, different bandsassociated with the wireless device 11 can operate using differentantennas.

In FIG. 22, one or more output signals from the transceiver 13 aredepicted as being provided to the antenna 14 via one or moretransmission paths 15. In the example shown, different transmissionpaths 15 can represent output paths associated with different bandsand/or different power outputs. For instance, the two example poweramplifiers 17 a, 17 b shown can represent amplifications associated withdifferent power output configurations (e.g., low power output and highpower output), and/or amplifications associated with different bands.Although FIG. 22 illustrates a configuration using two transmissionpaths 15 and two power amplifiers 17 a, 17 b, the wireless device 11 canbe adapted to include more or fewer transmission paths 15 and/or more orfewer power amplifiers.

In FIG. 22, one or more detected signals from the antenna 14 aredepicted as being provided to the transceiver 13 via one or morereceiving paths 16. In the example shown, different receiving paths 16can represent paths associated with different bands. For example, thefour example receiving paths 16 shown can represent quad-band capabilitythat some wireless devices are provided with. Although FIG. 22illustrates a configuration using four receiving paths 16, the wirelessdevice 11 can be adapted to include more or fewer receiving paths 16.

To facilitate switching between receive and transmit paths, the switches12 can be configured to electrically connect the antenna 14 to aselected transmit or receive path. Thus, the switches 12 can provide anumber of switching functionalities associated with operation of thewireless device 11. In certain embodiments, the switches 12 can includea number of switches configured to provide functionalities associatedwith, for example, switching between different bands, switching betweendifferent power modes, switching between transmission and receivingmodes, or some combination thereof. The switches 12 can also beconfigured to provide additional functionality, including filteringand/or duplexing of signals.

FIG. 22 shows that in certain embodiments, a control component 18 can beprovided for controlling various control functionalities associated withoperations of the switches 12, the power amplifiers 17 a, 17 b, thepower management system 30, and/or other operating components.

In certain embodiments, a processor 20 can be configured to facilitateimplementation of various processes described herein. The processor 20can implement various computer program instructions. The processor 20can be a general purpose computer, special purpose computer, or otherprogrammable data processing apparatus.

In certain embodiments, these computer program instructions may also bestored in a computer-readable memory 19 that can direct the processor 20to operate in a particular manner, such that the instructions stored inthe computer-readable memory 19.

The illustrated wireless device 11 also includes the power managementsystem 30, which can be used to provide power amplifier supply voltagesto one or more of the power amplifiers 17 a, 17 b. For example, thepower management system 30 can be configured to change the supplyvoltages provided to the power amplifiers 17 a, 17 b to improveefficiency, such as power added efficiency (PAE). The power managementsystem 30 can be used to provide average power tracking (APT) and/orenvelope tracking (ET). Furthermore, as will be described in detailfurther below, the power management system 30 can include one or morelow dropout (LDO) regulators used to generate power amplifier supplyvoltages for one or more stages of the power amplifiers 17 a, 17 b. Inthe illustrated implementation, the power management system 30 iscontrolled using a power control signal generated by the transceiver 13.In certain configurations, the power control signal is provided by thetransceiver 13 to the power management system 30 over an interface, suchas a serial peripheral interface (SPI) or Mobile Industry ProcessorInterface (MIPI).

In certain configurations, the wireless device 11 may operate usingcarrier aggregation. Carrier aggregation can be used for both FrequencyDivision Duplexing (FDD) and Time Division Duplexing (TDD), and may beused to aggregate a plurality of carriers or channels, for instance upto five carriers. Carrier aggregation includes contiguous aggregation,in which contiguous carriers within the same operating frequency bandare aggregated. Carrier aggregation can also be non-contiguous, and caninclude carriers separated in frequency within a common band or indifferent bands.

From the foregoing description, it will be appreciated that an inventivehexagonal ferrites and manufacturing methods are disclosed. Whileseveral components, techniques and aspects have been described with acertain degree of particularity, it is manifest that many changes can bemade in the specific designs, constructions and methodology herein abovedescribed without departing from the spirit and scope of thisdisclosure.

Certain features that are described in this disclosure in the context ofseparate implementations can also be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation can also be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations, one or more features from a claimed combination can, insome cases, be excised from the combination, and the combination may beclaimed as any subcombination or variation of any subcombination.

Moreover, while methods may be depicted in the drawings or described inthe specification in a particular order, such methods need not beperformed in the particular order shown or in sequential order, and thatall methods need not be performed, to achieve desirable results. Othermethods that are not depicted or described can be incorporated in theexample methods and processes. For example, one or more additionalmethods can be performed before, after, simultaneously, or between anyof the described methods. Further, the methods may be rearranged orreordered in other implementations. Also, the separation of varioussystem components in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described components and systems cangenerally be integrated together in a single product or packaged intomultiple products. Additionally, other implementations are within thescope of this disclosure.

Conditional language, such as “can,” “could,” “might,” or “may,” unlessspecifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include or do not include, certain features, elements,and/or steps. Thus, such conditional language is not generally intendedto imply that features, elements, and/or steps are in any way requiredfor one or more embodiments.

Conjunctive language such as the phrase “at least one of X, Y, and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require the presence of atleast one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms “approximately,”“about,” “generally,” and “substantially” as used herein represent avalue, amount, or characteristic close to the stated value, amount, orcharacteristic that still performs a desired function or achieves adesired result. For example, the terms “approximately”, “about”,“generally,” and “substantially” may refer to an amount that is withinless than or equal to 10% of, within less than or equal to 5% of, withinless than or equal to 1% of, within less than or equal to 0.1% of, andwithin less than or equal to 0.01% of the stated amount.

Some embodiments have been described in connection with the accompanyingdrawings. The figures are drawn to scale, but such scale should not belimiting, since dimensions and proportions other than what are shown arecontemplated and are within the scope of the disclosed inventions.Distances, angles, etc. are merely illustrative and do not necessarilybear an exact relationship to actual dimensions and layout of thedevices illustrated. Components can be added, removed, and/orrearranged. Further, the disclosure herein of any particular feature,aspect, method, property, characteristic, quality, attribute, element,or the like in connection with various embodiments can be used in allother embodiments set forth herein. Additionally, it will be recognizedthat any methods described herein may be practiced using any devicesuitable for performing the recited steps.

While a number of embodiments and variations thereof have been describedin detail, other modifications and methods of using the same will beapparent to those of skill in the art. Accordingly, it should beunderstood that various applications, modifications, materials, andsubstitutions can be made of equivalents without departing from theunique and inventive disclosure herein or the scope of the claims.

1. (canceled)
 2. A modified sodium substituted strontium hexagonalferrite comprising: a Y-phase strontium hexagonal ferrite crystalstructure including elements strontium, sodium, cobalt, iron, oxygen andone of a tetravalent ion and a trivalent ion, the at least one of thetetravalent ion and the trivalent ion configured to charge balance forthe sodium substituting at least partially for the strontium in thecrystal structure; and a permeability of between 5 and
 6. 3. Themodified sodium substituted strontium hexagonal ferrite of claim 2wherein the crystal structure contains the trivalent ion.
 4. Themodified sodium substituted strontium hexagonal ferrite of claim 3wherein greater than zero and less than or equal to 1.5 of the trivalention is included in the crystal structure.
 5. The modified sodiumsubstituted strontium hexagonal ferrite of claim 3 wherein the trivalention is selected from the group consisting of Al, Ga, Sc, Cr, Mn, In, Yb,Er, Y and lanthanide elements.
 6. The modified sodium substitutedstrontium hexagonal ferrite of claim 5 wherein the trivalent ion isscandium.
 7. The modified sodium substituted strontium hexagonal ferriteof claim 2 wherein the crystal structure contains the tetravalent ion.8. The modified sodium substituted strontium hexagonal ferrite of claim7 wherein greater than zero and less than or equal to 0.75 of thetetravalent ion is included in the crystal structure.
 9. The modifiedsodium substituted strontium hexagonal ferrite of claim 7 wherein thetetravalent ion is selected from the group consisting of Si, Ge, Ti, Zr,Sn, Ce, Pr, Hf, and Tb.
 10. The modified sodium substituted strontiumhexagonal ferrite of claim 2 wherein the modified sodium substitutedstrontium hexagonal ferrite has a compositionSr_(1.75)Na_(0.25)Co_(1.75)M_(0.25)Fe₁₂O₂₂, M being the trivalent ion.11. The modified sodium substituted strontium hexagonal ferrite of claim2 wherein the modified sodium substituted strontium hexagonal ferritehas a composition Sr_(1.5)Na_(0.5)Co_(1.5)M_(0.5)Fe₁₂O₂₂, M being thetrivalent ion.
 12. An antenna comprising: a Y-phase strontium hexagonalferrite crystal structure including elements strontium, sodium, cobalt,iron, oxygen and one of a tetravalent ion and a trivalent ion, the atleast one of the tetravalent ion and the trivalent ion configured tocharge balance for the sodium substituting at least partially for thestrontium in the crystal structure; and a permeability of between 5 and6.
 13. The antenna of claim 12 wherein the modified sodium substitutedstrontium hexagonal ferrite has a compositionSr_(1.75)Na_(0.25)Co_(1.75)M_(0.25)Fe₁₂O₂₂, M being the trivalent ion.14. The antenna of claim 12 wherein the modified sodium substitutedstrontium hexagonal ferrite has a compositionSr_(1.5)Na_(0.5)Co_(1.5)M_(0.5)Fe₁₂O₂₂, M being the trivalent ion. 15.The antenna of claim 12 wherein the trivalent ion is incorporated intothe crystal structure, the trivalent ion being scandium.
 16. Aradiofrequency device incorporating the antenna of claim
 12. 17. Amethod for improving properties of a hexagonal ferrite material, themethod comprising: providing a Y-phase strontium hexagonal ferrite witha crystal structure having strontium, cobalt, iron, and oxygen;substituting at least some of the strontium out of the crystal structureand replacing it with sodium; and charge balancing the hexagonal ferritematerial by incorporating one of a tetravalent ion and a trivalent ioninto the crystal structure to form a modified hexagonal ferrite materialhaving a permeability of between 5 and
 6. 18. The method of claim 17wherein the modified hexagonal ferrite has a compositionSr_(1.75)Na_(0.25)Co_(1.75)M_(0.25)Fe₁₂O₂₂, M being the trivalent ion.19. The method of claim 17 wherein the modified hexagonal ferrite has acomposition Sr_(1.5)Na_(0.5)Co_(1.5)M_(0.5)Fe₁₂O₂₂, M being thetrivalent ion.
 20. The method of claim 17 wherein the trivalent ion isincorporated into the crystal structure, the trivalent ion beingscandium.
 21. The method of claim 17 further including forming aradiofrequency device from the modified hexagonal material.